Dr Shand stressed that erosion hazard predictions were not certain, and a conservative approach was needed.

Based on his report, the council published predicted 50- and 100-year shoreline shifts in September, affecting 1800 properties. It placed the information on LIM reports for those properties on the same day.

Coastal Ratepayers United, whose membership includes economists, scientists, engineers and barristers, is challenging the report and wants the council to preserve and sustain the shoreline rather than its proposed "managed retreat" policy.

The council announced yesterday that about 80 properties south of Waikanae river mouth, formerly within the 50- to 100-year "unmanaged" erosion zone, would be managed by Greater Wellington regional council.

Economist and beachfront property owner Bryce Wilkinson questioned why the Shand report did not use the Environment Ministry's recommended predicted sea-level rises of 0.5 metres and 0.8m, instead using 0.9m. "Why did he also not use a lower figure of 0.6?" Dr Wilkinson asked.

Two Manly St residents, anthropologist Salima Padamsey and lawyer Christopher Ruthe, have questioned the science used and say residents should have been informed before the information became public and placed on LIMs.

"Any other council would have told the stakeholders exactly what was happening," Mr Ruthe said.

The group was looking at the legality of placing the information on LIMs and believed the council had "given in to a scientific report that failed to recognise the community's love of Kapiti as we know it".

He said the report was ultra-conservative "providing a worst-case climate-change scenario" that did not take accretion - areas of beach building up - into account.

The group has written to Local Government Minister David Carter, saying the issue should not be dealt with by small local councils.

All but one property owner walked out before council officers replied to their comments.

Mayor Jenny Rowan said the council had had a "real thumping".

"We are dealing with an intelligentsia, High Court judges, ex-Treasury, God knows what else. We are not here by choice . . . It was not our call; we had legal and policy obligations to meet.